Protective effect of 17beta-estradiol on ischemic acute renal failure through the PI3K/Akt/eNOS pathway

Estrogens attenuate renal injury induced by ischemia/reperfusion (I/R), an effect that is related to nitric oxide production in the post-ischemic kidney. The compound 17beta-estradiol (E(2)-beta) acting via estrogen receptors (ERs) is known to activate endothelial nitric oxide synthase (eNOS) through the phosphatidylinositol-3 kinase (PI3K)/Akt pathway. We determined if this pathway contributes to the renoprotective effect of E(2)-beta in the uninephrectomized ischemia reperfusion rat model of acute renal injury. Treatment with E(2)-beta suppressed the I/R-induced increases in blood urea nitrogen, plasma creatinine, urine flow, and fractional excretion of sodium while augmenting creatinine clearance, renal blood flow, and urine osmolality, indicating attenuation of renal injury. Phosphorylation of Akt and eNOS protein was significantly increased 30-60 min after reperfusion in estradiol-treated compared to vehicle-treated rats. The protective effects of E(2)-beta and protein phosphorylation were reversed by the PI3K inhibitor wortmannin or the ER antagonist tamoxifen. Furthermore, the E(2)-beta-induced renoprotective effects were not seen in eNOS knockout mice with renal injury. We conclude that the E(2)-beta-induced renoprotective effect is due to activation of the PI3K/Akt pathway followed by increased eNOS phosphorylation in the post-ischemic kidney.     

Isoflurane-induced myocardial preconditioning is dependent on phosphatidylinositol-3-kinase/Akt signalling

Background. Isoflurane and other volatile anaesthetics havea cardioprotective effect and limit myocardial infarct sizeto the same extent as ischaemic preconditioning. Phosphatidylinositol-3-kinase(PI3K) was found to play a key role in myocardial protectionby ischaemic preconditioning. The aim of the present investigationwas to evaluate whether isoflurane-induced myocardial preconditioningis dependent on PI3K signalling. Methods. Using a model of regional myocardial ischaemia andreperfusion, New Zealand White rabbits were subjected to 40min of regional myocardial ischaemia followed by 120 min ofreperfusion. The rabbits were randomly assigned to one of thefollowing six experimental groups: sham-operated controls (n=5);ischaemia and reperfusion controls (n=8); isoflurane preconditioning(n=8); a PI3K inhibitor, wortmannin (0.6 mg kg^–1 i.v.)+ isoflurane (n=8); and wortmannin+ischaemia and reperfusion(n=8). An additional control group of sham operation+ wortmannin(n=5) was also included. Myocardial injury was assessed by measuringthe serum concentration of the MB fraction of creatine kinase(CK-MB) and infarct size was assessed by 2,3,5-triphenyl tetrazoliumchloride staining. Phosphorylation of Akt, a downstream targetof PI3K, was assessed by western blotting. Results. Isoflurane preconditioning was seen as reduced infarctsize compared with control animals: 24 (4) and 41 (5)% respectively(P<0.05). Wortmannin inhibited this cardioprotective effectwith myocardial infarct size at 44 (3)% (not significant). Aktphosphorylation was increased after isoflurane preconditioning,but administration of wortmannin blocked this effect. Conclusions. Our data demonstrate that isoflurane protects theheart against ischaemia and decreases myocardial infarctionby activation of PI3K.     

Pretreatment with granulocyte colony-stimulating factor attenuated renal ischaemia and reperfusion injury via activation of PI3/Akt signal pathway

Aim: Granulocyte colony-stimulating factor (G-CSF) has been shown to exert protective effects in various tissues and experimental models of ischaemia-induced injury. However, the mechanism of renoprotective action in ischaemia/reperfusion (I/R) renal injury of G-CSF was unknown. Methods: Male C57BL/6J mice, subjected to renal ischaemia for 45 min, 48 h and 7 days reperfusion, were administered either saline, wortmannin, G-CSF, and G-CSF plus wortmannin 3 days prior to I/R. Saline-treated group served as the control. At 48 h and 7 days of reperfusion, the mice were killed. Results: Significantly, renal dysfunction and morphological injury were identified at 48 h and 7 days after I/R. Wortmannin pretreatment worsened the renal injury significantly. However, G-CSF pretreatment significantly attenuated renal injury, reduced the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive ratio of renal tubular epithelial cells and inflammation cytokine expression in the kidney. Moreover, G-CSF pretreatment inhibited the expression of Bax and increased the expression of bcl-2 and p-Akt in the kidney. Wortmannin blunted the beneficial effects of G-CSF. Conclusion: The cytoprotective action of G-CSF against I/R injury seems to be associated with its anti-apoptotic action mediated by upregulation of p-Akt signal pathway.     

Blockage of JAK/STAT signalling attenuates renal ischaemia-reperfusion injury in rat.

BACKGROUND: JAK/STAT signalling is one of the major pathways for cytokine signal transduction. However, the role of JAK/STAT in renal ischaemia/reperfusion (I/R) injury is not clear. The present study investigated the protection against renal I/R injury by in vivo inhibition of JAK2 activation. METHODS: Rats subjected to renal I/R were either treated with daily intraperitoneal injection of selective JAK2 inhibitor tyrphostin AG490 (10 mg/kg) or vehicle alone starting 4 h before, immediately after or until 3 h after I/R. Renal function, histology, infiltration of macrophages, apoptosis, expression of chemokines and adhesion molecules were assessed. RESULTS: AG490 treatment significantly inhibited the phosphorylation of JAK2 and its downstream molecule STAT1 and STAT3. Rats pretreated with AG490 exhibited improved renal function, attenuated histological lesions and reduced apoptosis of tubular epithelial cells. AG490 significantly inhibited renal expression of MCP-1 and ICAM-1 mRNA, as well as the expression of ICAM-1 protein, accompanied by decreased macrophage accumulation in the kidney. Immediate post-ischaemic treatment of AG490 also significantly ameliorated renal injury. However, delayed post-ischaemic treatment until 3 h after I/R failed to attenuate renal damage. CONCLUSIONS: This study demonstrated the involvement of JAK/STAT signalling in the pathogenesis of renal I/R injury, suggesting that JAK/STAT pathway may serve as a potential target for early intervention in ischaemic acute renal failure.     

Renal ischemia/reperfusion and ATP depletion/repletion in LLC-PK(1) cells result in phosphorylation of FKHR and FKHRL1

BACKGROUND: Cell death and survival pathways are critical determinants of epithelial cell fate after ischemia. Forkhead proteins have been implicated in the regulation of cellular survival. METHODS and RESULTS: We have found that none of the forkhead family of proteins, FKHR, is phosphorylated after ischemia/reperfusion in the rat kidney. The time course of phosphorylation is similar to the time course of activation of the forkhead protein kinase Akt/protein kinase B (PKB), with maximal phosphorylation at 24 to 48 hours postreperfusion when the process of regeneration peaks. Extracellular signal-regulated kinase (ERK)1/2 activation has also been implicated as prosurvival in the injured kidney. ERK1/2 were phosphorylated in postischemic kidneys at 5, 30, and 90 minutes of reperfusion, with phosphorylation decreased by 24 and 48 hours. Immunocytochemical analysis revealed increased phospho-ERK1/2 in the thick ascending limb and isolated cells of the S3 segment, which have lost apical actin staining. To understand the relationship between forkhead phosphorylation, Akt, and ERK1/2, an in vitro model of injury was employed. After 40 minutes of chemical anoxia followed by dextrose addition for 20 minutes to replete adenosine triphosphate (ATP) levels, FKHR and FKHRL1 are phosphorylated. The levels of phospho-Akt are increased for at least 120 minutes after dextrose addition with a maximum at 20 minutes. Phosphorylation of Akt, FKHR, and FKHRL1 are phosphatidylinositol 3-kinase (PI 3-kinase) dependent since phosphorylation is reduced by the PI 3-kinase inhibitors, wortmannin, or LY294002. Inhibition of mitogen-activated protein kinase (MAPK)/ERK kinase (MEK1/2), the upstream activator of ERK1/2, has no effect on forkhead protein phosphorylation after chemical anoxia/dextrose addition. CONCLUSION: We conclude that PI 3-kinase and Akt are activated after renal ischemia/reperfusion and that Akt phosphorylation leads to phosphorylation of FKHR and FKHRL1, which may affect epithelial cell fate in acute renal failure.     

Adiponectin protects skeletal muscle from ischaemia–reperfusion injury in mice through miR-21/PI3K/Akt signalling pathway

Previous studies have confirmed that adiponectin (APN) plays a protective role in myocardial ischaemia–reperfusion (IR) injury, and the aim of this study was to investigate its effect on skeletal muscle. ELISA was used to detect the levels of Creatinine Kinase (CK), LDH, SOD and MDA in the plasma of the lower limbs of mice, and the levels of IL-6, IL-1β and TNF-α in the gastrocnemius. Quantitative PCR was used to detect the expression level of miR-21. TUNEL staining was used to detect the apoptosis of the gastrocnemius. The expression levels of apoptosis proteins, autophagy marker proteins and downstream target genes of miR-21 in gastrocnemius were detected by Western Blot. The results of this study revealed that APN levels were significantly reduced in gastrocnemius of IR mice. The oxidative stress, inflammatory response, apoptosis and autophagy induced by IR were significantly ameliorated by APN injection. The above effects of APN may be achieved through miR-21/PI3K signalling pathway, as found by interfering gene expression levels with miRNA antagomir and lentiviral injection. Taken together, our study revealed that APN protects skeletal muscle from IR injury through miR-21 /PI3K/Akt signalling pathway through inhibiting inflammatory response, apoptosis and autophagy.     

Dexmedetomidine protects against myocardial ischaemia/reperfusion-induced renal damage in rats

Background

Myocardial ischaemia/reperfusion (MI/R) may induce renal damage. Our aim was to investigate the effects of dexmedetomidine (DEX) administration at two different timings either before or after ischaemia on renal damage induced by MI/R.

The phosphoinositide-3 kinase gamma-Akt pathway mediates renal tubular injury in cisplatin nephrotoxicity

Nephrotoxicity is a frequent complication of cisplatin-based chemotherapy often limiting its use. In this study, we attempted to the role of the phosphoinositide-3 kinase (PI3K)-gamma-Akt pathway in this form of acute kidney injury. Using PI3K-gamma knockout mice, we found that a conventional dose of cisplatin was more lethal in the knockout mice where the blood urea nitrogen and serum creatinine were significantly higher in them than in wild-type mice. Phosphorylation of Akt in the renal tubules was abrogated in the knockout mice with the severity of renal dysfunction and numbers of TUNEL (terminal deoxynucleotidyl transferase (TdT) mediated nick-end labeling)-positive renal tubule cells being higher in the knockout than in wild-type mice. Cisplatin treatment significantly increased. Caspase-3 activity, histone-associated DNA fragments, and number of annexin V-positive cells was significantly higher in cisplatin-treated primary cultured renal tubular epithelial cells of knockout mice. Transfection of dominant-active forms of Akt and PI3K-gamma ameliorated apoptosis of the tubule epithelial cells derived from the knockout mice. Our results suggest that the PI3K-gamma-Akt pathway lessens apoptosis and plays a critical role in the maintenance of renal function in cisplatin-induced acute kidney injury.     

PI3K/Akt信号通路在吡咯喹啉醌促雪旺细胞增殖中的作用

目的 探讨磷脂酰肌醇-3激酶/蛋白激酶B(phosphoinositide-3 kinase/Akt,PI3K/Akt)信号通路在吡咯喹啉醌促雪旺细胞增殖过程中的作用.方法 体外分离培养雪旺细胞,S-100免疫荧光鉴定;Western blot检测PI3K下游因子Akt磷酸化激活形式(p-Akt)的表达,并通过PI3K激酶抑制剂(wortmannin)阻断该通路后p-Akt的表达情况.结果 毗咯喹啉醌可使雪旺细胞发生形态学变化,加入吡咯喹啉醌后30 min即可检测到p-Akt的表达,4 h达高峰,12 h基本无表达;吡咯喹啉醌在1～100 nmol/L范围内可使p-Akt表达增加;加入wortmannin阻断PI3K后p-Akt上调表达消失(P<0.05).结论 吡咯喹啉醌可使雪旺细胞发生形态学变化,PI3K/Akt信号通路在吡咯喹啉醌促雪旺细胞增殖过程中发挥重要作用.     

Effect of apigenin on apoptosis induced by renal ischemia/reperfusion injury in vivo and in vitro

Objectives: This study aims to investigate the effects and molecular mechanisms of apigenin (ApI) on renal ischemia/reperfusion (I/R) injury in vivo and in vitro.

Methods: In vivo, the left renal artery was clamped for 45?min and the right kidney was removed to study renal I/R injury on Sprague-Dawley (SD) rats. ApI was injected at 60?min before renal ischemia. In vitro, renal tubular epithelial cells (HK-2) were pretreated with or without ApI (20 uM) for 60?min and then treated with hypoxia/reoxygenation (H/R). Renal function, histology, cells apoptosis, and cell viability were tested. Furthermore, the potential molecular mechanisms were assessed.

Results: ApI pretreatment could significantly alleviated the renal function and the pathological damage as well as cells apoptosis after I/R injury. Meanwhile, ApI treatment protects H/R induced HK-2 cell apoptosis in vitro. The results of Western blot showed that ApI significantly increased the expressions of B-cell lymphoma 2 (Bcl-2) and phosphor-AKt (p-AKt), Phosphoinositide 3-kinase (PI3K), while down-regulated the expressions of Caspase3 and Bax induced by H/R injury.

Conclusions: ApI pretreatment can protect renal function against I/R injury and prevent renal tubular cells from apoptosis in vivo and in vitro which might through PI3K/Akt mediated mitochondria-dependent apoptosis signaling pathway.     

Prevention of cold ischaemia-reperfusion injury by an endothelin receptor antagonist in experimental renal transplantation.

BACKGROUND: Endothelin (ET) is known to play a role in the pathogenesis of warm ischaemic renal damage, however, little is known about its involvement in renal cold ischaemia. This study was designed to investigate the response of ET after kidney cold ischaemia, and to assess the potential protective effect of bosentan, a dual, non-selective ET(A)/ET(B) receptor antagonist, against cold ischaemia reperfusion injury in a rat model of syngeneic renal transplantation. METHODS: Kidneys from Lewis rats were transplanted, either immediately or after 5 h of cold preservation. After 48 h, contralateral nephrectomy was performed. Rats were organized into three groups: Tr-NoISC, no cold ischaemia; Tr-ISC, 5 h cold ischaemia; and Tr-BOS, 5 h cold ischaemia plus bosentan (100 mg/kg/day, from the day before transplantation until the seventh day post-transplantation). On day 7, plasma and tissue immunoreactive ET (irET), as well as ET mRNA tissue expression, were evaluated. Renal function was measured by means of serum creatinine on days 3, 4, 5 and 7, and by creatinine clearance on day 7. Conventional histology was performed. RESULTS: The ischaemic group had significantly higher plasma irET levels than the non-ischaemic group and significantly lower levels than the bosentan group. Tissue irET levels and ET mRNA expression were similar in the ischaemic and bosentan groups and were higher than in the non-ischaemic group. Throughout the follow-up, serum creatinine was significantly higher in the ischaemic group than in the bosentan group. Moreover, creatinine decreased rapidly in the bosentan group after nephrectomy, whereas it continued to increase for 48 h in the ischaemic group. Kidneys from the ischaemic group showed a higher degree of tubular-cell necrosis and epithelial-cell detachment than kidneys from the bosentan group. CONCLUSIONS: We conclude that cold ischaemia and preservation damage induces an increase in renal ET mRNA and irET expression in the reperfusion phase, contributing both to the deterioration of renal function and to tubular necrosis. Bosentan is effective in protecting kidneys from this cold ischaemia reperfusion damage. Non-selective ET(A)/ET(B) receptor antagonists might be potentially useful in clinical renal transplantation.     

吗啡后处理对大鼠心肌缺血再灌注损伤的影响及PI3K/Akt信号通路在其中的作用

目的 评价吗啡后处理对大鼠心肌缺血再灌注损伤的影响及磷脂酰肌醇-3激酶,蛋白质丝氨酸苏氨酸激酶(PI3K/Akt)信号通路在其中的作用.方法 清洁级雄性SD大鼠70只,体重280～330 g,年龄16～17周.随机分为5组(n=14):假手术组(S组)、缺血冉灌注组(IR组)、吗啡后处理组(M组)、渥曼青霉素+吗啡后处理组(w+M组)和渥曼青霉素组(W组).采用结扎左冠状动脉前降支45 min、再灌注120 min的方法 制备心肌缺血再灌注模型.S组仅穿线,不结扎;M组于再灌注前3 min和再灌注后2 min时经左颈内静脉注射吗啡1.25 mg/kg;W+M组于结扎左冠状动脉前降支前20 min时经左颈内静脉注射PI3K特异性阻断剂渥曼青霉素15μg/kg,并行吗啡后处理;W组于结扎左冠状动脉前降支前20 min时经左颈内静脉注射渥曼青霉素15 μg/kg.于左冠状动脉前降支阻断前即刻、阻断20 min和再灌注120 min(T1-3)时记录心率(HR)、平均动脉压(MAP)和心率.收缩压乘积(RPP);于再灌注120 min时各组随机取9只大鼠,计算心肌缺血和梗塞范围;其余5只大鼠采用Western blot法测定心肌组织总Akt和磷酸化Akt的表达水平.结果 五组HR、MAP、RPP、心肌缺血范围和总Akt表达水平比较差异无统计学意义(P>0.05);与T1时比较,IR组、M组、S+M组和W组再灌注时MAP和RPP均降低(P<0.05);与S组比较,IR组和M组磷酸化Akt表达上调(P<0.05),W+M组和W组差异无统计学意义(P>0.05);与IR组比较,M组心肌梗塞范围缩小,心肌组织磷酸化Akt表达上调(P<0.01),W+M组和w组心肌梗塞范围差异无统计学意义(P>0.05).结论 吗啡后处理可减轻大鼠心肌缺血再灌注损伤,可能与进一步激活PI3K/Akt信号通路有关.     

Renoprotective effect of erythropoietin in ischemia/reperfusion injury: possible roles of the Akt/endothelial nitric oxide synthase-dependent pathway

Objectives: It has been reported that erythropoietin protects the kidneys from ischemia/reperfusion injury. In the present study, we examined the role of Akt and endothelial nitric oxide synthase in the protective effect of erythropoietin on ischemia/reperfusion injury of the kidney. Methods: Erythropoietin was injected in the peritoneal space of ICR mice after ischemia/reperfusion injury and its effect was assessed by measuring blood urea nitrogen and creatinine, and by histological analysis. Phosphorylation of Akt and endothelial nitric oxide synthase was examined by western blot analysis. Endothelial nitric oxide synthase gene null mice were also used to examine the role of endothelial nitric oxide synthase in the renoprotective effect of erythropoietin. Results: Erythropoietin administration significantly inhibited the increase in blood urea nitrogen and creatinine after ischemia/reperfusion injury compared with control mice. Accordingly, erythropoietin administration significantly ameliorated the histological damages, including apoptotic cell death. Erythropoietin significantly stimulated phosphorylation of Akt and endothelial nitric oxide synthase in the kidneys. When endothelial nitric oxide synthase gene null mice were subjected to ischemia/reperfusion injury, erythropoietin did not significantly suppress the increase in blood urea nitrogen or creatinine. Conclusions: Erythropoietin seems to activate the Akt/endothelial nitric oxide synthase‐dependent pathway in the kidneys. This pathway might be implicated in the renoprotective effect of erythropoietin in the ischemia/reperfusion injury model.     

PI3K/Akt信号通路在七氟醚后处理减轻大鼠局灶性脑缺血再灌注损伤中的作用

目的 评价磷脂酰肌醇3激酶/蛋白质丝氨酸苏氨酸激酶(PI3K/Akt)信号通路在七氟醚后处理减轻大鼠局灶性脑缺血再灌注损伤中的作用.方法 雄性SD大鼠64只,体重300～350 g,随机分为4组(n=16):局灶性脑缺血再灌注组(IR组)、七氟醚后处理组(SP组)、七氟醚后处理+Wortmannin组(SW组)和Wortmannin组(W组).采用电凝法阻断左侧大脑中动脉,夹闭双侧颈总动脉60 min恢复灌注的方法制备大鼠局灶性脑缺血再灌注模型.再灌注即刻SP组和SW组吸入2.5%七氟醚60 min,夹闭双侧颈总动脉30 min时SW组和W组股静脉输注Wortmannin 0.6 mg/kg.于再灌注24、48、72 h时行神经功能评分,最后1次评分后处死大鼠取脑,测定脑梗死体积,采用Western blot法检测左侧脑组织磷酸化Akt(p-Akt)和磷酸化Bad(p-Bad)的表达水平.结果 与IR组相比,SP组和SW组各时点神经功能评分升高,再灌注72 h时脑梗死体积比降低,脑组织p-Akt和p-Bad表达上调(P＜0.05),W组上述指标差异无统计学意义(P＞0.05);与SP组相比,SW组各时点神经功能评分降低,再灌注72 h时脑梗死体积比升高,脑组织p-Akt和p-Bad表达下调(P＜0.05).结论 PI3K/Akt信号通路激活后p-Bad表达上调可能参与了七氟醚后处理减轻大鼠局灶性脑缺血再灌注损伤的过程.     

The influence of Phosphatidylinositol 3-kinase/Akt Pathway on the Ischemic Injury during Rat Liver Graft Preservation

We aimed to investigate the role of phosphatidylinositol 3 (PI3)-kinase/Akt pathway on ischemic injury. Rat liver grafts were preserved in UW solution with different treatments and were compared by 1-week survival rates and morphological changes with those of the control group. PI3-kinase/Akt was significantly activated at the sites of Thr 308 and Ser 473 in the preserved grafts. Downstream target proteins, glycogen synthase kinase-3beta (GSK-3beta) and caspase-9, were inactivated. However, survival signal transduction from Akt to Bad was blocked by calcium release after activation of PI3-kinase/Akt. Significant activation of caspase-12, -3 and -7 contributed to cell apoptosis and severe ischemic injury was shown after 7 h of preservation by UW solution with insulin. Downregulation of phospho-Akt at Thr 308 and Ser 473 was due to partial inhibition of PI3-kinase/Akt pathway by LY294002. Activation of GSK-3beta and inactivation of caspase-12 and Bad could be found in the LY294002 groups in which the liver grafts showed less ischemic injury. Higher 1-week survival rates in the heparin, LY294002, and glucagon groups confirmed the dysregulation of the pathway. In conclusion, PI3-kinase/Akt pathway was dysregulated and contributed to ischemic injury during preservation. Heparin and LY294002 could improve graft viability by maintaining calcium homeostasis during preservation.     

Activation of renal signaling pathways in db/db mice with type 2 diabetes

BACKGROUND: Altered regulation of signaling pathways may contribute to the pathogenesis of renal disease. We examined renal cortical signaling pathways in type 2 diabetes. METHODS: The status of renal cortical signaling pathways was examined in control and db/db mice with type 2 diabetes in the early phase of diabetic nephropathy associated with renal matrix expansion and albuminuria. RESULTS: Tyrosine phosphorylation of renal cortical proteins was increased in diabetic mice. Renal cortical activities of phosphatidylinositol 3-kinase (PI 3-kinase) in antiphosphotyrosine immunoprecipitates, Akt (PKB), and ERK1/2-type mitogen-activated protein (MAP) kinase activities were significantly augmented sixfold (P < 0.01), twofold (P < 0.0003), and sevenfold (P < 0.001), respectively, in diabetic mice compared with controls. A part of the increased renal cortical PI 3-kinase activity was due to insulin receptor activation, as PI 3-kinase activity associated with beta chain of the insulin receptor was increased nearly fourfold (P < 0.0235). Additionally, the kinase activity of the immunoprecipitated insulin receptor beta chain was augmented in the diabetic renal cortex, and tyrosine phosphorylation of the insulin receptor was increased. In the liver, activities of PI 3-kinase in the antiphosphotyrosine immunoprecipitates and Akt also were increased threefold (P < 0.05) and twofold (P < 0.0002), respectively. However, there was no change in the hepatic insulin receptor-associated PI 3-kinase activity. Additionally, the hepatic ERK1/2-type MAP kinase activity was inhibited by nearly 50% (P < 0.01). CONCLUSIONS: These studies demonstrate that a variety of receptor signaling pathways are activated in the renal cortex of mice with type 2 diabetes, and suggest a role for augmented insulin receptor activity in nephropathy of type 2 diabetes.     

Isoflurane Protects against Myocardial Infarction during Early Reperfusion by Activation of Phosphatidylinositol-3-Kinase Signal Transduction: Evidence for Anesthetic-induced Postconditioning in Rabbits

Background: Brief episodes of ischemia during early reperfusion after coronary occlusion reduce the extent of myocardial infarction. Phosphatidylinositol-3-kinase (PI3K) signaling has been implicated in this "postconditioning" phenomenon. The authors tested the hypothesis that isoflurane produces cardioprotection during early reperfusion after myocardial ischemia by a PI3K-dependent mechanism.

Methods: Pentobarbital-anesthetized rabbits (n = 80) subjected to a 30-min coronary occlusion followed by 3 h reperfusion were assigned to receive saline (control), three cycles of postconditioning ischemia (10 or 20 s each), isoflurane (0.5 or 1.0 minimum alveolar concentration), or the PI3K inhibitor wortmannin (0.6 mg/kg, intravenously) or its vehicle dimethyl sulfoxide. Additional groups of rabbits were exposed to combined postconditioning ischemia (10 s) and 0.5 minimum alveolar concentration isoflurane in the presence and absence of wortmannin. Phosphorylation of Akt, a downstream target of PI3K, was assessed by Western blotting.

Results: Postconditioning ischemia for 20 s, but not 10 s, reduced infarct size (P < 0.05) (triphenyltetrazolium staining; 20 +/- 3% and 34 +/- 3% of the left ventricular area at risk, respectively) as compared with control (41 +/- 2%). Exposure to 1.0, but not 0.5, minimum alveolar concentration isoflurane decreased infarct size (21 +/- 2% and 43 +/- 3%, respectively). Wortmannin abolished the protective effects of postconditioning (20 s) and 1.0 minimum alveolar concentration isoflurane. Combined postconditioning (10 s) and 0.5 minimum alveolar concentration isoflurane markedly reduced infarct size (17 +/- 5%). This action was also abolished by wortmannin (44 +/- 2%). Isoflurane (1.0 minimum alveolar concentration) increased Akt phosphorylation after ischemia (32 +/- 6%), and this action was blocked by wortmannin.     

Isoflurane protects against myocardial infarction during early reperfusion by activation of phosphatidylinositol-3-kinase signal transduction: evidence for anesthetic-induced postconditioning in rabbits

BACKGROUND: Brief episodes of ischemia during early reperfusion after coronary occlusion reduce the extent of myocardial infarction. Phosphatidylinositol-3-kinase (PI3K) signaling has been implicated in this "postconditioning" phenomenon. The authors tested the hypothesis that isoflurane produces cardioprotection during early reperfusion after myocardial ischemia by a PI3K-dependent mechanism. METHODS: Pentobarbital-anesthetized rabbits (n = 80) subjected to a 30-min coronary occlusion followed by 3 h reperfusion were assigned to receive saline (control), three cycles of postconditioning ischemia (10 or 20 s each), isoflurane (0.5 or 1.0 minimum alveolar concentration), or the PI3K inhibitor wortmannin (0.6 mg/kg, intravenously) or its vehicle dimethyl sulfoxide. Additional groups of rabbits were exposed to combined postconditioning ischemia (10 s) and 0.5 minimum alveolar concentration isoflurane in the presence and absence of wortmannin. Phosphorylation of Akt, a downstream target of PI3K, was assessed by Western blotting. RESULTS: Postconditioning ischemia for 20 s, but not 10 s, reduced infarct size (P < 0.05) (triphenyltetrazolium staining; 20 +/- 3% and 34 +/- 3% of the left ventricular area at risk, respectively) as compared with control (41 +/- 2%). Exposure to 1.0, but not 0.5, minimum alveolar concentration isoflurane decreased infarct size (21 +/- 2% and 43 +/- 3%, respectively). Wortmannin abolished the protective effects of postconditioning (20 s) and 1.0 minimum alveolar concentration isoflurane. Combined postconditioning (10 s) and 0.5 minimum alveolar concentration isoflurane markedly reduced infarct size (17 +/- 5%). This action was also abolished by wortmannin (44 +/- 2%). Isoflurane (1.0 minimum alveolar concentration) increased Akt phosphorylation after ischemia (32 +/- 6%), and this action was blocked by wortmannin. CONCLUSIONS: Isoflurane acts during early reperfusion after prolonged ischemia to salvage myocardium from infarction and reduces the threshold of ischemic postconditioning by activating PI3K.